This invention relates to a method for preparing a gas-supersaturated emulsion or suspension and delivering it from high pressure environment to a gas-depleted site without the immediate onset of cavitation or bubbling.
The maximum concentration of gas achievable in a liquid is governed by Henry""s Law. The relatively low solubility at ambient pressure of many gases (for example, oxygen or nitrogen) within a liquid such as water results in a low concentration of the gas in the liquid when these are mixed. There are, however, many applications where it would be advantageous to employ a gas in a liquid mixture where the concentration of the gas within the liquid greatly exceeds its solubility at ambient pressure.
High-pressure compression of a liquid within a liquid emulsion or solid within a liquid suspension can be used to achieve a higher dissolved gas concentration, but disturbance of this gas supersaturated liquid through ejection into a 1 bar environment from the high pressure reservoir will generally result in cavitation inception at or near the exit port. The rapid evolution of bubbles produced at the exit port vents much of the gas from the liquid, so that the high degree of gas concentration within the liquid is considerably reduced at the ambient pressures outside the high pressure vessel. Additionally, the presence of bubbles in the effluent generates turbulence and impedes the flow of the effluent beyond the exit port.
A wide variety of applications would benefit from ejection of a gas-supersaturated fluid from a high pressure reservoir into an ambient pressure environment in a manner which does not involve cavitation inception at or near the exit port. For example, organic material and plant waste streamsxe2x80x94e.g., paper mills and chemical plantsxe2x80x94often require an increase in dissolved oxygen content before these streams can be safely discharged into a body of water. U.S. Pat. No. 4,965,022 recognizes that a similar need may also occur at municipal waste treatment plants and that fish farms require increased dissolved oxygen levels to satisfy the needs of high density aquaculture. Other applications are disclosed in U.S. Pat. No. 5,261,875.
There are many prior art references which disclose methods of enriching the oxygen content of water. For example, U.S. Pat. No. 4,664,680 discloses several conventional types of apparatus that can be used for continuously contacting liquid and oxygen-containing gas streams to effect oxygen absorption within the liquid. Specifically, pressurizable confined flow passageways are used to avoid premature liberation of the dissolved oxygen before it is incorporated within the fluid. Other oxygen saturation devices are disclosed in U.S. Pat. Nos. 4,874,509 and 4,973,558. However, these techniques leave unsolved the problem of how to eject the gas-enriched fluid solutions from a high pressure reservoir into a lower pressure environment without the formation of bubbles in the effluent at or near the exit port.
In a previous application, Ser. No. 08/581,019, filed Jan. 3, 1996, I describe a method for ejection of gas-supersaturated liquids from a high pressure to a low pressure environment without cavitation, consisting of extrusion of the fluid through capillary channels and compression to remove cavitation nuclei along the inner surface of the channels. Hydrostatic compression at pressures between 0.5 kbar and 1.0 kbar rapidly removes cavitation nuclei and bubbles from the liquid. When a gas source is used to both pressurize the liquid and achieve a desired concentration of a relatively insoluble gas in the liquid, it is generally necessary to maintain the gas pressure in the 10 bar to 150 bar range.
The complete absence of cavitation inception in water saturated with oxygen at high concentrations permits its in vivo infusion into either venous or arterial blood for the purpose of increasing the oxygen concentration of the blood while avoiding the formation of bubbles which tend to occlude capillaries.
In contrast to this capillary channel technique, the present invention dispenses with the necessity of compressing fluids within capillary channels, relying instead on use of gas-supersaturated emulsions and suspensions.
A method is described for the use of emulsions or suspensions to transport a gas-supersaturated liquid from a high pressure reservoir to a relatively low pressure environment (including ambient pressure), without immediate cavitation inception.
If a liquid that has a relatively high gas solubility (also known as the internal phase) is suspended in fine droplets within another immiscible liquid or semi-solid having a relatively low gas solubility (known as the carrier or external phase) a high level of supersaturation of the gas can be achieved in the resulting emulsion upon its release to a gas-depleted environment at ambient pressure. Likewise, solid particles can be suspended within a liquid carrier to form a suspension with the same properties (unless otherwise indicated, the descriptions for liquid in liquid emulsions are true for solid in liquid suspensions as well). The primary gases of interest for the formation of gas supersaturated emulsions are oxygen, nitrogen, and carbon dioxide.
The small size of the droplets or particles in conjunction with exposure to a transient high hydrostatic pressure confers stability to the droplets or particles in a manner similar to that provided by small diameter capillary. tubes. Generally, the fine droplets are between about 0.1 micron and about 10 microns in diameter. Thus, after release of the emulsion to an ambient pressure environment, the gas that is dissolved at high levels of supersaturation will not form bubbles, despite a relatively high concentration of the gas within the droplets or particles.
The carrier of the droplets or particles is stable at high gas partial pressures because of the relatively low gas solubility of the carrier as well as the absence of gas nuclei after hydrostatic compression. A low gas diffusion coefficient in the carrier results in a slow, delayed release of the gas both from the droplets or particles to the carrier as well as from the emulsion to the gas-depleted environment. Despite this slow release of gas from the emulsion and the relatively low concentration of gas in the carrier, the high partial pressure of gas in the emulsion creates a high driving pressure gradient between the emulsion and gas-poor surfaces.
As a result of the lack of cavitation inception at or near the exit port, a stream of the gas-supersaturated emulsion can be used to rapidly and efficiently enrich a gas-deprived site such as a liquid by convection of the emulsion to the gas-deprived site. Enrichment of a gas-deprived liquid with gas by diffusion from the gas phase to the liquid is, by contrast, an extremely slow process.
The lack of bubbles in the effluent additionally permits unimpeded ejection into the gas-depleted site. When the gas-supersaturated emulsion is ejected in an air environment, the lack of cavitation inception at or near the exit port allows the effluent to behave as if it were not supersaturated with gas. That is, the ejected stream remains intact rather than disintegrating into a diffuse spray near the exit port due to the rapid growth of gas nuclei.
The basic steps for forming the gas-supersaturated emulsion (the same method applies to the formation of a gas-supersaturated suspension) are: preparing the emulsion; exposing the emulsion to a gas at a pressure greater than 2 bar; and delivering the emulsion to a gas-depleted environment at ambient pressure. Typically, the emulsion is exposed to the gas (the primary gas of interest is oxygen) at a pressure of between about 5 bar and about 20 bar. The emulsion could be rapidly mixed (at about 1600 rpm, for instance) for several hours during its exposure to the gas at partial pressures between 100 psi and 1500 psi. Additionally, the emulsion could be delivered to a high pressure hydrostatic pump in order to further increase the partial pressure of the gas.
The emulsion is extruded at the output of a pressurizable vessel through a tube, which delivers the emulsion to the outside environment at between about 0.1 and about 10 ml per minute.
This type of emulsion can be used to efficiently deliver oxygen to the skin, to wounds, or to other environments. In a biological context, the high level of oxygen achieved in such tissues by contact of the emulsion with the tissues should be helpful in a variety of ways, such as collagen synthesis, inhibition of anaerobic bacterial growth, and promotion of aerobic metabolism. A supersaturated oxygen emulsion can also be used to oxygenate blood for a variety of medical applications. The emulsion is injected directly into the bloodstream, thereby increasing oxygen delivery to the blood.